1. Technical Field
The present invention relates to a rotor type open-end spinning unit and a rotor driving method therefor.
2. Related Background Art
Open-end spinning units which do not require a roving process by a roving frame are popular due to the improved productivity and possible cost reduction concerning the facility investment or the like. Of the open-end spinning units, a rotor type is the oldest and has been proved reliable.
In this rotor type open-end spinning unit, a supplied sliver is opened by a combing roller and, at the same time, foreign matter is expelled. The opened fibers are supplied into a rotor in high speed rotation by an airstream created in the fiber transport channel due to the negative pressure in the rotor, and are collected at a fiber-collecting section, a portion of the rotor with the largest inner diameter. The fiber bundle at the fiber-collecting section is drawn out by a draw roller from a yarn drawing passage, provided on the open side of the rotor on the same axial line as the rotor, while being twisted, and wound as a package around a bobbin. More specifically, the fiber bundle forced out from the fiber-collecting section is drawn along the inner wall of the yarn drawing passage. At this time, the fiber bundle is drawn out while rotating along the inner wall of the yarn drawing passage due to the friction against that wall with the rotation of the rotor. This applies temporary twisting to the fiber bundle to help achieve the actual twisting.
The fiber bundle collected at the fiber-collecting section is however stuck on the inner wall of the fiber-collecting section only by the centrifugal force created by the rotation of the rotor. The fiber bundle drawn along the yarn drawing passage is thus twisted. This twisting propagates to the fiber bundle still stuck on the fiber-collecting section, causing the fiber bundle therein to rotate.
At the time of fiber twisting, therefore, sufficient tensile strength cannot be obtained so that the fibers would be twisted in a loose state. As a result, the fibers are not twisted stretched or in a tensed manner, weakening the yarn strength.
As a solution to this shortcoming, an apparatus as disclosed in Japanese Unexamined Patent Publication No. 51-64034 (see FIGS. 36 and 37) has been proposed. This apparatus has a disk-shaped draft rotor 93 provided inside an outer rotor 92 which has a fiber-collecting section 91. The draft rotor 93 makes a differential rotation to the outer rotor 92. The draft rotor 93 has a hole formed in its center in which a yarn guide duct (yarn drawing duct) 94 is loosely fitted. This hole perpendicularly intersects a draw hole 95 from which a fiber bundle F collected at the fiber-collecting section is drawn out. The draft rotor 93 is provided with a small disk 96 (shown in FIG. 37) which revolves while being pressed against the fiber bundle collected in the fiber-collecting section which also rotates.
In this apparatus, the draft rotor 93 rotates faster than the outer rotor 92 while having a predetermined rotational difference (a difference of almost 50 to several hundred turns per minute) with the outer rotor 92 to draw the fiber bundle F collected in the fiber-collecting section 91 through the draw hole 95. The fiber bundle F is therefore spun while being applied with a draft. Further, the fiber bundle F is spun while being drafted with the floating of the fiber bundle F being regulated by the action of the small disk 96.
Since this apparatus drafts the fiber bundle F while twisting it, however, the fibers on the fiber-collecting section 91 behave unstably, causing a variation in the thickness of the spun yarn. In other words, as the fiber bundle is drafted, some fibers are pulled while the rest stay unstretched, varying the thickness of the yarn. With fibers in different lengths as shown in FIG. 38, longer fibers f.sub.L are pulled, the rear end of a shorter fiber f.sub.s may be bent as shown in FIG. 39, reducing the yarn strength.
In addition, this apparatus has difficulty in keeping the small disk 96 rotating while being pressed against the fiber bundle F. Further, as the small disk 96 faces the fiber-collecting section 91, it is difficult for the opened fibers to enter the fiber-collecting section 91 when the small disk 96 comes to a position corresponding to the opening of the fiber supply passage. This state occurs every time the draft rotor 93 makes one turn, causing a variation in the fiber bundle F collected at the fiber-collecting section 91. This may not only cause the yarn to be cut frequently when spinning but also will reduce the quality of the spun yarn.
Japanese Unexamined Patent Publication No. 57-56528 discloses an apparatus as shown in FIG. 40. In this apparatus, an inner rotor 97 located inside an outer rotor 92, which has a fiber-collecting section 91, makes a differential rotation with respect to the outer rotor 92.
A spinning chamber 98 is provided in the inner rotor 97, with a fiber suction pipe 99 provided in the spinning chamber 98 to suck the fiber bundle F collected at the fiber-collecting section 91. As compressed air is supplied into the spinning chamber 98 via a hollow support shaft 100, an air vortex is generated. At the same time, the fiber bundle F collected at the fiber-collecting section 91 is sucked into the spinning chamber 98 via the fiber suction pipe 99 and is twisted due to the air vortex into yarn. Then, the yarn Y is expelled together with the expelling airstream toward a draw roller 101, and is drawn out by that roller 101.
However, this apparatus has a complicated inner-rotor structure and is difficult to manufacture. In addition, this apparatus is provided with no means to prevent the twisting applied on the fiber bundle F by the air vortex from propagating to that fiber bundle F which is still stuck on the fiber-collecting section 91. The twisting is thus applied to the fibers while the fibers are not sufficiently tense. Therefore, this apparatus still has the aforementioned conventional problem of not twisting the fibers in a stretched condition, preventing the yarn strength from being increased. Further, this apparatus uses inefficient compressed air that is used to generate inside the spinning chamber 98 of the inner rotor 97 an air vortex which has enough suction force to provide the fiber suction pipe 99 with a suction action to suck the fiber bundle F collected at the fiber-collecting section 91 of the outer rotor 92.